If I understand the FX5200 - it does provide full DX9 functionality, but with a lot of software assistance to a fairly weak hardware - in AGP, it would be a budget card.
As I understand it, the Pixel shaders are in hardware, but slow unless Nvidia cheats on benchmarks, with the vertex shaders and other stuff heavily software assisted.
But until some maker is crackers enough to put a better chipset on PCI, it's the ONLY DX9 upgrade that will fit a PCI slot.
http://www.ebuyer.com/customer/produ...duct_uid=61650 - £66.40 at ebuyer
http://www.dabs.com/uk/productview?quicklinx=2VK0 Different brand, cheaper - seems to be about the ballpark for them though